Continued function of the corpus luteum beyond its normal two-week life span is necessary for the maintenance of pregnancy in monkeys and women, yet little is known about the factors which regulate the life span and endocrine activity of the corpus luteum in primates. The research outlined in this proposal is designed to obtain basic knowledge about the mechanisms involved in regression of the primate corpus luteum during the non-fertile menstrual cycle. It has been hypothesized that estrogen synthesized by the corpus luteum initiates the process of luteal regression. To address this hyypothesis we will examine the effects of estrogen on progesterone secretion and protein synthesis by isolated luteal cells maintained in culture. In addition, we will use density gradient fractionation techniques to identify different populations of cells in the monkey corpus luteum. We have obtained evidence that serum concentrations of biologically active luteinizing hormone (LH) decline just prior to luteolysis in rhesus monkeys. In the second part of the study we will attempt to determine the reasons for the decline in LH concentrations and whether or not this decline plays a role in spontaneous luteolysis. To this end, we will compare the pulse frequency and amplitude of LH concentrations and whether or not this decline plays a role in spontaneous luteolysis. To this end, we will phase with that of the middle and late luteal phase. Second, we will compare the pulse frequency and amplitude of LH release during the early luteal examine the effects of progesteroone on serum levels of biologically active LH and the life span of the corpus luteum. Third, we will determine the effects of maintenance of early luteal phase levels of LH on function of the corpus luteum. Fourth, we will compare the biological and immunological activities of circulating LH during the luteal phase. In the last part of the study we will investigate the possible role of prostaglandins in regression of the primate corpus luteum. Prostaglandin F2 Alpha and prostaglandin E2 in ovarian venous plasma during spontaneous and estrogen-induced luteolysis will be measured. Finally, we will examine prostaglandin synthesis and uptake by isolated luteal cells in vitro. We feel that these studies will provide novel and important information about the function of the primate corpus luteum.